A fluid becomes supercritical when it is compressed to a pressure and elevated to a temperature greater than that of its critical point. Supercritical fluids (SCFs) exhibit properties of both a liquid and a gas. An SCF has a relatively high liquid-like density, and because solubility usually increases with density and pressure, SCFs have a high absorption capacity. The gas-like properties of high diffusivity and low viscosity allow for high mass transfer rates between a solute and an SCF. SCFs having a high rate of absorption are widely used in organic compound extraction.
Supercritical fluid extraction (SFE) is the process of separating a component or compound from a source material (also referred to as a “matrix,” a “raw material,” and the like) using supercritical fluids as a solvent. The source material may be a solid or liquid material. In many cases, the compound may be a desired product, such as a lipid, essential oil, and the like. In other cases, the compound could be an undesired product, for example, caffeine for decaffeinated coffee products. Devices used to extract compounds from source materials may be referred to as SFE apparatuses.
Many SFE apparatuses use supercritical carbon dioxide (CO2) as a solvent for the extraction of compounds. Such SFE apparatuses typically include a pump that is powered by an air compressor, a CO2 supply that may include one or more tanks of CO2, a heating element, a single extraction chamber, an air cooling device, and a single collection chamber. Extraction techniques using the typical SFE apparatuses may include filling the extraction chamber with source material and pumping CO2 into the extraction chamber. Prior to entering the extraction chamber, the CO2 may enter a compressor to be compressed and heated until it reaches the supercritical phase. In some cases, a heating element may heat the extraction chamber so that the CO2 enters the supercritical phase while inside the extraction chamber. The supercritical CO2 becomes saturated with a compound as it moves through the extraction chamber and comes into contact with the source material. The supercritical CO2 saturated with a compound may be referred to as a “composition.” The composition may then flow into the collection chamber where the composition drops in pressure. The drop in pressure causes the CO2 to enter a liquid phase and separate from the compound. At this point, the compound may enter a liquid or solid phase depending on the chemical characteristics of the compound. The liquid CO2 may then be “burned off” as a gas to be vented or re-condensed in a storage tank for recirculation. These collection chambers may be referred to as “two phase collection chambers” because the solvent undergoes two phase changes while inside the collection chamber. Once the compound is completely extracted from the source material, the SFE apparatus undergoes a decompression operation so that the material remaining in the extraction chamber may be removed, and new source material may be placed into the extraction chamber. Once new source material is placed in the extraction chamber, the extraction process may start again by pumping new or recycled CO2 into the extraction chamber. The decompression operations and the compression operations of most SFE apparatuses may relatively time consuming. For example, most SFE apparatuses take approximately one hour to decompress to a point where the extraction chamber may be opened. Additionally, from the decompressed state, most SFE apparatuses take approximately 20-30 minutes to compress the CO2 to enter the supercritical phase. The aforementioned process may be referred to as a “batch operation.”
The amount of compound(s) that may be extracted using typical SFE apparatuses and typical extraction methods may be limited by the chemical properties of the source material and/or the chemical properties of the compound sought to be extracted. The properties of the source material and/or the compound may inform the amount of solvent to be used and/or an amount of processing time required for extracting the compound(s). For example, compounds that are heavy fatty acids, such as cannabinoids, may be difficult to solubilize using a typical SFE solvent, such as CO2. Source materials comprising such compounds may require relatively large quantities of solvents and/or relatively long processing times for extraction of these compounds. Currently, the typical extraction methods using the typical SFE apparatuses are insufficient to meet the current demand for extracts due to the relatively long processing times. Furthermore, because the typical extraction methods using the typical SFE apparatuses include burning off gaseous CO2, the end product obtained using the typical extraction methods may include some contaminants because such contaminants may be too heavy to burn off with the gaseous CO2.
One technique used to reduce processing times includes increasing a size or volume of the extraction chamber so that the extraction chamber may hold more source material than smaller extraction chambers. Since a larger extraction chamber may hold more source material, some processing time may be saved in reducing a number of times that the SFE apparatus has to be decompressed. However, increasing the size and/or volume of an extraction chamber does not increase the rate of extraction because the rate of extraction is dependent on the flow rate of the solvent. Furthermore, increasing the size and/or volume of the extraction chamber may dramatically increase manufacturing costs associated with constructing the extraction chamber. This is because, in order to keep the CO2 in the supercritical phase, a thickness of the extraction chamber walls needs to increase as the extraction chamber becomes larger. Therefore, in many cases, the costs associated with constructing a relatively large extraction chamber may outweigh the perceived benefits. Another technique used to reduce processing times includes increasing a flow rate of the solvent in order to achieve a higher rate of extraction. However, increasing the flow rate of the solvent usually requires a larger and/or more powerful pump to be used in the SFE apparatus. Because more powerful pumps typically consume more energy (i.e., fossil fuels) than less powerful pumps, operating costs associated with operating a more powerful pump may be prohibitive. Furthermore, in typical SFE apparatuses, the flow rate is required to match the burn off rate of the solvent. In these cases, increases in the flow rate may be limited because of the time required for liquid solvents to undergo a phase change and burn off as a gas, for example, CO2 entering a collection chamber as a liquid and being burned off as a gaseous CO2. Yet another technique used to reduce processing times includes using cosolvents, such as ethanol and/or hexane, in addition to CO2 to speed up the saturation rate of the supercritical CO2 thereby increasing the rate of extraction. However, the use of cosolvents may introduce contaminates into the extracted compound(s). Moreover, using cosolvents may require extensive post-processing in order to purify the extracted compound. This extensive post-processing may also require additional pumps and chemical additives, which may increase the costs associated with using cosolvents.
In addition to relatively long processing times, another drawback associated with typical SFE apparatuses includes environmental degradation. As mentioned previously, after the compound separates from the supercritical CO2, the CO2 may enter a gaseous phase and is then vented, thereby releasing CO2 into the atmosphere. Even if the gaseous CO2 is condensed and recirculated through the SFE apparatus, once the compound is completely extracted from the source material, the SFE apparatus is decompressed, thereby releasing CO2 into the atmosphere. This is due to the limiting factor that typical SFE apparatuses containing two phase collection chambers are relatively slow due to the time required for re-condensing solvents from a gaseous state back to a liquid state for recirculation. Therefore, by allowing the gaseous solvent to be released into the atmosphere, an overall processing time may be decreased. However, as is known, the release of CO2 into the atmosphere contributes to anthropogenic climate change, which may contribute to sea level rise, extreme weather, and/or other like negative environmental impacts.